Two different types of such tow chains are mainly used, namely chains whereby the links are joined together in a hingeable manner by means of horizontally placed shafts and chains whereby the links are joined together in a hingeable manner by means of vertically placed shafts, whereby said second type of chains are also provided with rotor wheels placed on the shafts according to a particular embodiment.
The known first type of tow chains has a good bending around a horizontal rotary shaft, but its main disadvantage is that it only allows for a restricted bending around a vertical rotary shaft, due to the required minor play between the horizontal chain shafts and the chain links.
If such a chain of the first type has to undergo a bending in a horizontal plane, an impractically large rotary radius is required in certain cases.
Since these chains usually consist of a number of links with vertical cheeks which are joined together at the top by means of a closing wall, it is clear that the dirt, which accumulates in the rail between the chain cheeks, will be pushed up between these cheeks at a particular moment and will be carried along, one and other such that at the height of a driving gear, bending gear respectively, of such a tow chain, the teeth of such gear will successively press together the dirt in these U-shaped links as a result of which, after a while, on the chain on the one hand and on the gear on the other hand, unwanted forces are exerted which cause the chain to wear out and/or disturb the correct gripping of the teeth of the driving gear in the respective links.
The tow chains of said second type have as a main disadvantage that the bottommost cheeks of half of the links are dragged along the bottom of the above-mentioned rail, which results in a relatively significant wear of the cheeks concerned on the one hand and, after the cheeks have worn out to a certain point, a relatively significant wear of the end concerned of the vertical chain shafts on the other hand.
It is clear that this soon diminishes the strength of the chain.
Another disadvantage of a tow chain of the above-mentioned second type consists in that the dirt which accumulates in the rail in which such chain is moved can only be removed with great difficulty since only the thin side edges of the cheeks of the different links, which are placed side by side, scrape over the bottom of the rail and thus only push the dirt over a limited width such that it is heaped up so to say along the side edges of the chain links.
Yet another disadvantage of this second type of chains consists in that, as the dirt is pushed forward by the above-mentioned cheeks, this dirt is pushed directly against the vertical chain shafts and ends up between these shafts and their bearing, which naturally results in an early wear of these shafts.
In the case where such a second type of chains are provided with rotor wheels placed on the chain shafts, the dirt also ends up between these wheels as a result of the propulsion, which provokes wear on the one hand and causes the wheels to become stuck on the other hand, which provokes even more wear.